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- Feb 1, 2015
- Messages
- 9,568
The resolution will kill you. You are essentially measuring angular rotation as determined by movement around a circumference. For any angular movement, the movement on the circumference is proportional to the radius of said circumference. A sensor mounted on a 2.5" radius will have to be four times more accurate than the accuracy at the spindle, 10" out.
Linear scales do not use a single point for sensing. They have a ruled scale with regular spacing and the sensor picks up a change from light to dark, low capacitance to high capacitance, etc. to generated pulses which are then accumulated to determine position
I have designed an optical system for homing my CNC mill which is repeatable to +/- .0001" and could be modified for your needs. I used an Omron OPB829DZ optointerupter, combined with regulated emitter LED current, comparison to a regulated reference voltage via an LM311 comparator, and well designed optics. This provides consistent positioning to within +/- .0001", the resolution of my Tormach DRO.
The Omron optointerupter has a narrow window for better collimation of the led light beam. My design used a sharp knife edge to block the beam, generating the signal. This resulted in a steep voltage ramp as the knife edge moved to block the beam. This voltage was then compared to a stable reference voltage to generate the trigger signal.
You still have the issue of magnification of error so your ultimate resolution may only be +/- .0005" at best and possibly worse.
Linear scales do not use a single point for sensing. They have a ruled scale with regular spacing and the sensor picks up a change from light to dark, low capacitance to high capacitance, etc. to generated pulses which are then accumulated to determine position
I have designed an optical system for homing my CNC mill which is repeatable to +/- .0001" and could be modified for your needs. I used an Omron OPB829DZ optointerupter, combined with regulated emitter LED current, comparison to a regulated reference voltage via an LM311 comparator, and well designed optics. This provides consistent positioning to within +/- .0001", the resolution of my Tormach DRO.
The Omron optointerupter has a narrow window for better collimation of the led light beam. My design used a sharp knife edge to block the beam, generating the signal. This resulted in a steep voltage ramp as the knife edge moved to block the beam. This voltage was then compared to a stable reference voltage to generate the trigger signal.
You still have the issue of magnification of error so your ultimate resolution may only be +/- .0005" at best and possibly worse.